1. Field of the Invention
The present invention relates to the polymerization of molten lactide (either S or R) using an yttrium or lanthanide series rare earth metal based catalyst.
2. Description of the Related Art
Lactides are presently polymerized to high molecular weight plastics using stannous 2-ethylhexanoate (tin octanoate) as the catalyst by ring opening polymerization of the cyclic ester: ##STR1## These polymers of lactide are useful in medical applications such as wound closure devices, orthopedic implants, and controlled release drug carriers.
U.S. Pat. No. 5,028,667 discloses the polymerization of various lactones including lactide using yttrium and lanthanide series rare earth based catalysts.